What size bolt holds fixed shifter rod.

[mph1001]

1989 SHO, the bolt that holds the fixed shifter rod to the trans stripped. It was converted to a rod shifter by the previous owner. I just want to make sure they used the right bolt. It's a M12 x 1.75 - 5" long. It doesn't seem to thread in very far, and even a tap/thread chaser only goes about half way in. Looks like I'm going to end up putting a HeliCoil in it.

Thanks, David.